1 files changed, 91 insertions, 0 deletions
diff --git a/compiler/rustc_passes/src/weak_lang_items.rs b/compiler/rustc_passes/src/weak_lang_items.rs
new file mode 100644
index 000000000..c48b4ecf8
--- /dev/null
+++ b/compiler/rustc_passes/src/weak_lang_items.rs
@@ -0,0 +1,91 @@
+//! Validity checking for weak lang items
+
+use rustc_data_structures::fx::FxHashSet;
+use rustc_errors::struct_span_err;
+use rustc_hir::lang_items::{self, LangItem};
+use rustc_hir::weak_lang_items::WEAK_ITEMS_REFS;
+use rustc_middle::middle::lang_items::required;
+use rustc_middle::ty::TyCtxt;
+use rustc_session::config::CrateType;
+
+/// Checks the crate for usage of weak lang items, returning a vector of all the
+/// language items required by this crate, but not defined yet.
+pub fn check_crate<'tcx>(tcx: TyCtxt<'tcx>, items: &mut lang_items::LanguageItems) {
+    // These are never called by user code, they're generated by the compiler.
+    // They will never implicitly be added to the `missing` array unless we do
+    // so here.
+    if items.eh_personality().is_none() {
+        items.missing.push(LangItem::EhPersonality);
+    }
+    if tcx.sess.target.os == "emscripten" && items.eh_catch_typeinfo().is_none() {
+        items.missing.push(LangItem::EhCatchTypeinfo);
+    }
+
+    let crate_items = tcx.hir_crate_items(());
+    for id in crate_items.foreign_items() {
+        let attrs = tcx.hir().attrs(id.hir_id());
+        if let Some((lang_item, _)) = lang_items::extract(attrs) {
+            if let Some(&item) = WEAK_ITEMS_REFS.get(&lang_item) {
+                if items.require(item).is_err() {
+                    items.missing.push(item);
+                }
+            } else {
+                let span = tcx.def_span(id.def_id);
+                struct_span_err!(
+                    tcx.sess,
+                    span,
+                    E0264,
+                    "unknown external lang item: `{}`",
+                    lang_item
+                )
+                .emit();
+            }
+        }
+    }
+
+    verify(tcx, items);
+}
+
+fn verify<'tcx>(tcx: TyCtxt<'tcx>, items: &lang_items::LanguageItems) {
+    // We only need to check for the presence of weak lang items if we're
+    // emitting something that's not an rlib.
+    let needs_check = tcx.sess.crate_types().iter().any(|kind| match *kind {
+        CrateType::Dylib
+        | CrateType::ProcMacro
+        | CrateType::Cdylib
+        | CrateType::Executable
+        | CrateType::Staticlib => true,
+        CrateType::Rlib => false,
+    });
+    if !needs_check {
+        return;
+    }
+
+    let mut missing = FxHashSet::default();
+    for &cnum in tcx.crates(()).iter() {
+        for &item in tcx.missing_lang_items(cnum).iter() {
+            missing.insert(item);
+        }
+    }
+
+    for (name, &item) in WEAK_ITEMS_REFS.iter() {
+        if missing.contains(&item) && required(tcx, item) && items.require(item).is_err() {
+            if item == LangItem::PanicImpl {
+                tcx.sess.err("`#[panic_handler]` function required, but not found");
+            } else if item == LangItem::Oom {
+                if !tcx.features().default_alloc_error_handler {
+                    tcx.sess.err("`#[alloc_error_handler]` function required, but not found");
+                    tcx.sess.note_without_error("use `#![feature(default_alloc_error_handler)]` for a default error handler");
+                }
+            } else {
+                tcx
+                    .sess
+                    .diagnostic()
+                    .struct_err(&format!("language item required, but not found: `{}`", name))
+                    .note(&format!("this can occur when a binary crate with `#![no_std]` is compiled for a target where `{}` is defined in the standard library", name))
+                    .help(&format!("you may be able to compile for a target that doesn't need `{}`, specify a target with `--target` or in `.cargo/config`", name))
+                    .emit();
+            }
+        }
+    }
+}